The cross continent connectivity is not going to be particularly
reliable. Prone to cuts due to wars and regional turmoil. And
imagine how it takes to repair problems at the physical layer.
I think that view is too myopic... you make it sound like Namibia,
Botswana, Zimbabwe and Zambia are at war. Just like all other
continents, unrest exists in some states, not all of them.
For the regions the OP is interested in, there isn't any conflict
there that would prevent him from deploying network.
Terrestrial connectivity is not a viable solution because:
It costs too much.
Different countries (even direct neighbors) do not share
social, economic or political values.
Most of the available network is in the hands of incumbents,
typically controlled by the gubbermint.
It costs too much.
There isn't sufficient capacity to drive prices down when
crossing 2 or more countries.
It costs too much.
Many markets are closed off and it's impossible to obtain
licenses to compete.
It costs too much.
Much of the network is old and has barely been upgraded.
It costs too much.
For those bold enough to build, the terrain in some parts is
not a walkover.